The Changes Of Extracellular Polymeric Sludge And Their Effects On The Characteristics Of The Sludge In The Process Of Biological Treatment Of Landfill Leachate

Landfill leachate is a kind of high concentration organic wastewater and difficult to be degraded.At present,the biological method is firstly used to remove the target pollutants in landfill leachate and then the wastewater can achieve standard discharge treatment through the membrane technology.Therefore,the sludge aggregates are crucial of the biological treatment process.The extracellular polymeric substance(EPS)are formed by the metabolism of microorganism and have significant impacts on the physical and chemical characteristics of sludge aggregates As a result,the treatment efficiency of the bioreactor will be affected.However,the composition and content of EPS can be influenced by the changes of process conditions such as salinity,aeration rate and so on.In this work using activated sludge process to treat landfill leachate,the variations of EPS from the activated sludge at different conditions(salinities and aeration rates)and their effects on microbial cell aggregation were investigated.The compositions of EPS and cell aggregation in aerobic and anaerobic sludge were also compared.The conclusions are as followed:(1)The contents of PN and PS in LB-EPS and TB-EPS increased with the increase of salinity,but the amounts of PS increased more than PN.Due to the increase of EPS contents,the sludge volume index(SVI)increased,while the hydrophobicity of sludge decreased.In addition,the results also indicated that the structure of flocs became looser with the increase of salinity,while the zeta potentials of the activated sludge were affected by EPS and salinity,showing a trend of increasing firstly and then decreasing.(2)Three-dimensional excitation-emission matrix(3D-EEM)fluorescence spectra showed that as salinity increased,functional groups with hydrophilicity and negative zeta potential in the EPS increased.Analysis of the amide I region of the protein spectrum at 1700-1600cm-1 showed that the relative contents of secondary structure of ?-antiparallel sheets in loosely bounded EPS proteins increased,while the proportion of loose protein structure in LB-EPS decreased as the salinity increased.Overall,these changes of EPS resulted in a decrease in microbial cell aggregation.Meanwhile,the microbial cell surfaces presented more negative zeta potentials upon the extraction of cations in EPS.The results suggested that the mechanism of EPS facilitated cell aggregation is mainly due to charge neutralization.Although the changes in EPS composition reduced the potential of cell aggregation at high salinity,the high capability of cell aggregation upon EPS extraction indicated the salinity could at least partially compensate the aforementioned effect by double layer compression.(3)With the increase of aeration intensity,the contents of tryptophan protein-like and aromatic protein-like substances increased,while the contents of fulvic-like and humic acid-like substances decreased.The relative content of protein secondary structures of?-turn increased,while the value of ?-helix/(?-sheets+ random coil)showed an downward trend as the aeration intensity increased.The results also suggested the the structure of EPS will be looser with the increase of aeration intensity and the hydrophobic sites inside the protein molecule were exposed more easily at higher aeration rates,which would be in favor of microbial cell aggregation and maintaining stable sludge structure.(4)Compared with the EPS components in system of salinity change,the protein secondary structures of ?-turn were the main form in aeration system and the values of?-helix/(?-sheets+ random coil)were lower.Therefore,the EPS structures were looser in aeration system.(5)The result of 3D-EEM fluorescence spectra showed the EPS in anaerobic sludge had more content of fulvic-like and humic acid-like substances than EPS in aerobic sludge,and its components were more complex than aerobic sludge.The result of FTIR showed anaerobic sludge contained more contents of PS substances and relative content of protein secondary structures of ?-helix and ?-sheets,while contained less relative content of protein secondary structures of ?-antiparallel sheets and ?-turn.The zeta potentials of aerobic sludge showed an increased trend,while the anaerobic sludge showed a decreased trend upon EPS extraction.The aggregation experiment suggested the aggregation rates of aerobic sludge were higher than anaerobic sludge and the aggregation rates had a good relationships with the values of ?-helix/(?-sheets+ random coil).